This invention relates to magnetic recording media and in particular to the structure of the magnetic layer.
There are many different forms of mass data storage technology used in modern computing. One of the prevailing forms of data recording is magnetic data recording due to its large capacity and re-usable recording media. Magnetic data recording may be implemented utilizing different types of magnetic recording media, including tapes, hard disks, floppy disks, etc. There is an ever increasing need for magnetic recording media with higher storage capacity, lower noise, and lower costs.
Magnetic recording media can be longitudinal magnetic recording media or, more recently, perpendicular magnetic recording media. Perpendicular recording media have many advantages over longitudinal recording media and are currently the more preferred magnetic recording media.
The structure of a typical perpendicular magnetic recording disk is multilayered and includes a substrate at its base covered by one or more underlayers such as soft magnetic underlayers followed by a hard magnetic layer and optionally, additional protective layer(s) on top of the magnetic layer. The protective overcoat protects the magnetic recording layer from corrosion and reduces frictional forces between the disc and a read/write head. In addition, a thin layer of lubricant may be applied to surface of the protective overcoat to enhance the tribological performance of the head-disc interface by reducing friction and wear of the protective overcoat.
The composition of a hard magnetic layer can vary but can include such compounds as FePt or CoPt as described, for example, in US Patent Appln. Publication US2004/0191578 to Chen et al. The quality of the magnetic layer is in part determined by the layer or layers between the substrate and the magnetic layer. Important magnetic properties, for example, coercivity which are crucial to the recording performance of a disk can depend, for example, on the microstructure of the various underlayers.
Granular perpendicular magnetic recording media has been developed for its capability of further extending the areal density of stored data, as compared to conventional perpendicular media, which is limited by the existence of strong lateral exchange coupling between magnetic grains. A granular perpendicular recording medium comprises a granular perpendicular magnetic layer having magnetic columnar grains separated by grain boundaries.
The grain boundaries provide a substantial reduction in the magnetic interaction between the magnetic grains. The grain boundary materials determine, to a large degree, the magnetic grain size, boundary width, exchange coupling strength between grains, etc., hence they play a key role in the recording performance of the media. Currently, grain boundary materials include a single additive compound that improves a particular feature of the magnetic layer. For example, in a FePt granular media, MgO can be used as the grain boundary additive because it provides a smooth media surface.